This invention is in the technical field of detection of a vehicle. In particular, this invention relates to an apparatus for and a method of detecting an object in front of one's own vehicle and recognizing it as a vehicle, capable of identifying an object as a vehicle with a high level of accuracy without being confused by other objects of various kinds that may be present. Such an apparatus and a method may be applied to a cruise control system, contributing significantly to its reliability.
As disclosed in Japanese Patent Publication Koho 3,264,060, for example, there have been known vehicle control systems adapted to carry out an image processing operation on an image of conditions in front of one's own vehicle by means of a camera so as to recognize a front-going vehicle and to control the engine output for operating the vehicle so as to trail this front-going vehicle. Since the image taken by the camera includes various background images in addition to that of the front-running vehicle, it is required to correctly recognize only a desired object (or the front-running vehicle) out of all these background images.
In view of this requirement, aforementioned Japanese Patent Publication Koho 3,264,060 discloses a method of initially transmitting a laser beam from a laser radar in a forward direction while scanning within a horizontal plane, receiving reflected laser beam at the same time to thereby obtain position data of an object in front of one's own vehicle, next using an image processor to make a “processing area” within the image narrower for an object at a greater distance corresponding to the position coordinate of the object detected by the laser radar, shifting the processing area to the left or to the right as the position of the object is displaced in the direction of the width of one's own vehicle, and recognizing a front-going vehicle by carrying out image processing on the image of the processing area.
According to this method, in summary, the existence of an object in front is recognized first from a reflected laser beam of the laser radar and the focus of attention on the image obtained by the camera (referred to as the “processing area”) is narrowed according to the result of recognition by the laser radar (the position of the object) such that only the image of this small area where the existence of a front-going vehicle is considered probable is processed without being confused by unnecessary background images such that only the desired target object (the front-going vehicle) can be correctly recognized.
By this prior art method, since a narrowed processing area is selected according to a result of recognition by the laser radar and only the image in this narrowed processing area is processed, it may be hoped that a front-going vehicle can be thereby recognized more accurately without being confused by the various background images. For reasons to be described below, however, this prior art method has a room for improvement regarding its accuracy of recognition.
According to the method of aforementioned Japanese Patent Publication Koho 3,264,060, areas surrounded by vertical lines are extracted from an image taken by a camera and the area having a symmetrical image in the left-right direction which does not move significantly from one to the next of images that are sequentially taken in is recognized as containing the image of a front-going vehicle. This criterion, and in particular the criterion related to symmetry, is too rough and hence there is a high probability that an object other than a vehicle may be erroneously recognized as a vehicle.
Consider a situation where one's own vehicle is traveling in the lane on the farthest left-hand side and there is another vehicle running in front at about the same speed in the next lane on the right-hand side. In this situation, this vehicle in a different lane cannot be an object of trailing. If the road makes a sharp curve to the left, the vehicle in the neighboring lane may show its side view almost exact in front of the own vehicle. In other words, the vehicle in a different lane may come to satisfy the condition according to this prior art technology for being a front-going vehicle that may be trailed because many vehicles are nearly symmetrically shaped when viewed from one side. Such a situation is likely to adversely affect the reliability of such an apparatus.